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Science for grade 7 Chapter - 8

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Presentation on theme: "Science for grade 7 Chapter - 8"— Presentation transcript:

1 Science for grade 7 Chapter - 8
Acids, Bases and Salts Science for grade 7 Chapter - 8

2 Module Objectives Define acids, bases and salts.
Differentiate between acids and bases Know uses of common acids, bases and salts Define indicators Explain neutralization reaction Explain pH value

3 ACIDS Acids are sour to taste.
The word acid comes from the Latin word acidus, meaning sour. Foods that contain acids: Citrus fruits like lemon, orange, gooseberry, Vinegar Tamarind Milk Curd A bee sting or the bite of a red ant produces a burning sensation because these insects inject Formic acid into the body when they sting or bite.

4 Mineral (inorganic) Acids
Types of Acids Acids Organic Acids Mineral (inorganic) Acids Acids that are prepared from minerals present in the earth are called mineral acids Examples: Sulphuric acid - H2SO4 Hydrochloric acid - HCl Nitric acid - HNO3 Acids that occur naturally are called organic acids Examples: Organic Acid Occurs in Citric acid lemon, orange Tartaric acid tamarind, grapes Lactic acid milk

5 Parts of an acid An acid has two parts –the hydrogen part and the radical part. A radical is a charged group of atoms. When acids dissolve in water, they split up into their hydrogen part and radical part. Acid Hydrogen part Radical part HCl H+ Cl- H2SO4 2H+ SO42- HCl Dissolves in H20 H Cl- hydrogen ion chloride ion Dissolves in H20 2H SO42- H2SO4 hydrogen ion sulphate ion

6 Definition An Acid is a compound which when dissolved in water gives hydrogen ions (H+) as the only positive ion.

7 Physical Properties of Acids
Taste Sour Conductivity Acid in water makes water a good conductor of electricity Solubility Soluble in water. Dissolving acid in water is an exothermic reaction, i.e it gives out heat. Corrosiveness Very corrosive. Acids can destroy paper, wood, metals and cause burns on skin. Litmus Effect Blue litmus turns Red.

8 Chemical Properties of Acids

9 Chemical Properties of Acids

10 Uses of Acids Hydrochloric Acid (HCl) Nitric Acid (HNO3)
To manufacture glue To purify common salt In preparation of glucose and chlorides For bleaching in textile industry Nitric Acid (HNO3) To etch designs on metals To purify gold and silver To extract metals from their ores In the manufacture of dyes, perfumes, fertilizers, explosives

11 Uses of Acids Sulphuric Acid (H2SO4) Carbonic Acid Aqua Regia
To refine petrol To manufacture detergents, plastics, paint In paper and automobile industry Carbonic Acid To prepare soft drinks Aqua Regia To etch designs on gold and platinum

12 BASES Chemical compounds that are bitter to taste are called bases.
A base has two parts- metal part and hydroxyl part Base Metal part Hydroxyl part Na (OH) Na+ (OH)- Ca (OH)2 Ca2+ 2(OH)- Na(OH) Dissolves in H20 Na (OH)- sodium ion hydroxide ion

13 Types of Bases All bases do not dissolve in water ALKALI NON-ALKALI
Bases that dissolve in water Bases that do not dissolve in water Sodium hydroxide Aluminium hydroxide Potassium hydroxide Copper hydroxide

14 Physical Properties of Bases
Taste Bitter Feel Soapy to touch Conductivity Good conductor of electricity Corrosiveness Some bases are corrosive Litmus Effect Red litmus turns Blue

15 Chemical properties Base + Acid Salt + Water Calcium hydroxide
Sulphuric Acid Calcium sulphate + Water + Sodium hydroxide Hydrochloric Acid Sodium chloride + + Water

16 Uses of bases Sodium hydroxide ( NaOH ) Calcium hydroxide ( Ca(OH)2 )
In textile, plastic industry To manufacture medicine, paper To refine petroleum Calcium hydroxide ( Ca(OH)2 ) In white washing As an antidote for acid poisoning In manufacture of bleaching powder, cement To remove fur from animal skin Ammonium hydroxide ( NH4OH ) Remove ink from clothes and grease stains

17 Indicators Indicators are chemical substances to indicate if a substance is acidic, basic or neutral. Example: Litmus ACID BASE

18 Indicators

19 Neutralization Acids react with bases to form respective salts and water. This reaction is called a neutralization reaction. Base Acid Salt + Water

20 Acid – Base Comparison

21 SALTS Salts are prepared by the neutralization reaction of acids and bases Base Acid Salt + Water

22 Properties of salts Most salts are solids with high melting and boiling point Most salts are soluble in water Salts that dissolve in water make the solution a good conductor of electricity

23 Some important salts Sodium chloride Sodium carbonate
Sodium bicarbonate Copper sulphate Potassium nitrate Potash alum Silver nitrate

24 Sodium chloride – Common Salt
Added to food Used in pickling and curing of fish and meat Used in pottery glazing

25 Sodium carbonate – Washing soda
To wash clothes To refine petroleum In manufacture of detergents, paper and glass

26 Sodium bicarbonate – Baking Soda
In bakery products like bread and cakes As an antacid In fire extinguishers

27 Other salts Copper sulphate Potassium nitrate Potash Alum
To manufacture medicines Potassium nitrate In glass and refrigeration industries Potash Alum In purification of water Silver Nitrate In developing films

28 pH value The acidity or basic strength of substances can be measured using a special scale called the pH scale. Most Acidic Most Basic

29 Importance of pH The pH range suitable for the human body is 7 to 7.8
Stomach produces HCl pH ranges in different parts of the body is shown below

30 Exercises Choose the correct answer

31 Exercises

32 Exercises

33 Exercises

34 Exercises

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